Any one of a set of constants, also known as elastic moduli, that defines the properties of material that undergoes stress, deforms, and then recovers and returns to its original shape after the stress ceases. The elastic constants include the bulk modulus, Lame constant, Poisson's ratio, shear modulus, and Young's modulus. Elastic constants are important in seismology because the velocity of waves depends on the elastic constants and density of the rock.